This invention relates to an output amplifying circuit for use in audio equipment.
The output amplifying circuit is a so-called power amplifier in audio equipment. Heretofore, a variety of power amplifiers have been proposed, for example Class A or Class B Push Pull amplifiers (hereinafter referred to it merely as Class A, or Class B PP amplifier when applicable) is typical of such power amplifiers.
Provided in the Class A complementary PP amplifier are a pair of output transistors which are continuously operated in the unsaturated conductive state. Accordingly, these output transistors cannot shift their states from unsaturated conductive states to cut-off states, and therefore the Class A complementary PP amplifier is advantageous in that no switching distortion will occur. In this case, however, a well known disadvantage exists in that, since a relatively large biasing current is required, heat loss may become excessively large.
In contrast, the Class B complementary PP amplifier is advantageous in that, a biasing current is smaller than that of the aforementioned Class A complementary PP amplifier. As a result, the heat loss can be positively decreased. However, it has a disadvantage that the output transistors are alternately turned-on or turned-off. This causes the switching distortion to occur. Also, both the Class A and the Class B complementary PP amplifiers have antipodal characteristics.